Question

When a motor car of mass 1500 kg is pushed on a road by two persons, it moves with a small
uniform velocity. On the other hand, if this car is pushed on the same road by three persons, it
moves with an acceleration of 0.2 m/s?. Assume that each person is producing the same muscular
force. Then, the force of friction between the tyres of the car and the surface of the road is :
(A) 300N
(B) 600N
(C) 900N
(D) 100N

Answer 1

Answer:option B

Explanation:

I have attached a solution

Answer 2

Answer:

B) 600 N

Explanation:

Given

Mass of motor car, M = 1500 kg

Accⁿ when pushed by 3 person, a = 0.2m/s²

Calculation

Let us assume that F is the force produced by a person and let f be the force of friction.

case 1 - car moves uniformly when pushed by 2 person. So 2F is just enough to overcome the frictional force.Hence

2F = f .............(1)

case 2 - car moves with acceleration when pushed by 3 person. So,

3F - f = Ma .......(2)

or 3F - 2F = 1500*0.2

or F = 300 N

Substituting value of F in (1) we get

f = 2*300

or f = 600 N